LU-4788 lfsck: enable verification for remote object

Based on the LFSCK 1.5 framework, enable the namespace LFSCK
scanning for remote object.

During the first-stage scanning, if the object contains remote
linkEA entry or multiple linkEA entries or claims as multiple
linked, then it will be recorded in the namespace LFSCK tracing
file for double scanning.

Some cleanup for the namespace LFSCK tracing file (lfsck_namespace)
and other code cleanup.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ibc87ae9a5c6b7f67a9215140cf2cb89640bce0a9
Reviewed-on: http://review.whamcloud.com/11317
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>